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Why do some of our engines have different Oberdorfer sea water pumps than others, and what about that cir-clip "holding on the impeller"?

The first part pertains more to M-25s with Oberdorfer pumps, than to M-25XPs -- but it's interesting background anyway... The second part pertains to us all with Oberdorfer pumps.....

Here's the impeller/shaft mismatch, cir-clips stories....

Grease cups are on engines with the Ob 202M-03 and 202M-07 series pumps (which were also used on some of our Universals), but no grease cups are on the 202M-15 and 202M-16 series pumps.

Back in the heyday of a boat-a-day per boat mfgr, Universal bought whatever model pumps were available from whatever sources they could get them (OB, SW) and made do. Remember, "standard" is a word that the marine industry never embraced. So to meet the demand for engines -- remember 1 boat/day with "X" manufacturers = a crap load of demand for engines.

So, Universal fabricated a special adapter plate and shaft adapter w/ male-male ends (3 pics below) to use the female shaft (M-03/07) pumps on some of our female-socketed Universals (our camshaft end has a female fork [see 1st pic below] to accept the male end of an optional hour meter on the Kubota tractors.) Yes, that's what the "pump land" on our gear covers is there for -- not a pump -- but a mechanical hour meter for the tractor.)

When removing the pump impeller and shaft, it's usually a simple matter of reinserting/rotating the shaft/impeller until the male tang on the shaft lines up w/ the fork on the camshaft. But with the Universals that had the M-03/07 pumps, the male-male shaft adapter would remain inside the gear cover and then be misaligned when sliding the shaft/impeller back in (the adapter had to fit OVER the end of the shaft AND align with the female fork.)
Because pump body blocks the view, one didn't know what the problem was, and blue streaks were oftentimes seen emanating from below and a purple haze floated above companionways along the dock. Luckily I had removed my M-07 pump first (not pulled the impeller/shaft alone,) so I saw the deal and never pulled just the shaft.

About the Oberdorfer cir-clip "holding" the impeller on the shaft, here's the story....

Back in the dark `90s when I replaced my Universal adapter plate, male-male shaft adapter, and Oberdorfer 202M-07 pump - with an Ob 202M-15 model, my Engineer-side saw that the cir-clip "holding" the impeller was "doing nothing." (I sure don't want to be hunting for my cir-clip pliers in an emergency.) But the young-n-dumb diesel-engine-novice side said, "Before I trash this clip, I want the expert(s') opinion(s') on why not to do that."

I went 'round n 'round with factory techs about the cir-clip and no one could fabricate a reasonable explanation why it was there.

--- "It holds the impeller in place"
(Nah, not necessary -- the pump cover does that.)

--- "It keeps the shaft in place."
(Try again, the shaft rides against the camshaft and can't "exit" the pump.)

As determined as they were with their BS, they couldn't get rid of me or the nagging question that begged for an answer -- "Why would Oberdorfer spend good money to machine a groove into the shaft and buy cir-clips -- unless there's a reason for it?"

Out of sheer frustration I guess, or maybe to play a trick on a co-worker, they passed this idiot asking the unanswerable question onto another old-tymer's phone extension.
It backfired -- he had been at Oberdorfer long enough and was honest enough to reveal the truth. Ob must have had issues with the pump shafts coming out whilst pumps were knocked about in shipping (Nah, "Brown" wouldn't do that) and thrown about in warehouses (Really?) and the cir-clip holds the shaft in the pump it's bolted in place.

--- "Yes you're right, it's unnecessary to have it on there and you can remove it...but we don't tell customers that."'